This invention relates to the field of magnetic data recording and, more particularly, to a method for duplicating data on a rotating magnetic disk.
Publishers of consumer software must make many copies of their works for distribution and sale to the public. Efficient use of the duplicating equipment is an important consideration in software publishing because of the cost of production. A commonly used medium for distributing consumer software is a floppy disk on which the data is stored in modified frequency modulation (MFM) format so that data is organized on concentric tracks in sectors referenced to an index mark. As a result, the sectors of all the tracks are aligned with each other, e.g. physical sector 3 starts at the same angular displacement from the index mark and ends at the same angular displacement from the index mark. Conventional techniques for duplicating data on a floppy disk in MFM format are synchronized to start duplicating each track at the index mark and thus require three revolutions to duplicate each track--the first revolution to record the data, the second revolution to check the data, and the third revolution to move the recording head to the next track and wait for the index mark to start recording the data on the next track. Most of the third revolution represents unproductive time because the head can step to the next track in a fraction of the time it takes for the disk to rotate one complete revolution. Thus, the duplicating equipment remains idle for the better part of the third revolution while waiting for the index mark.
In some floppy disk recording formats, such as Mcintosh and Amiga, this idle time is eliminated by starting to record data beginning with sector 1, as soon as the head is repositioned on a new track. As a result, data is recorded with sector skew, i.e., the sectors are not referenced to an index, as in MFM recording. In other words, a particular sector may appear at any one of a number of positions on a track, depending upon when the head arrives at such track. Sector skewing violates the rules for MFM format and is therefore not acceptable.